Add PoolAllocator class

[jslee02]

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Before creating a pull request

• Document new methods and classes
• Format new code files using ClangFormat by running make format
• Build with -DDART_TREAT_WARNINGS_AS_ERRORS=ON and resolve all the compile warnings

Before merging a pull request

• Set version target by selecting a milestone on the right side
• Summarize this change in CHANGELOG.md
• Add unit test(s) for this change

[codecov]

Codecov Report

Merging #1645 (6161fd7) into main (4041649) will increase coverage by 0.05%.
The diff coverage is 68.78%.

@@            Coverage Diff             @@
##             main    #1645      +/-   ##
==========================================
+ Coverage   59.06%   59.11%   +0.05%     
==========================================
  Files         491      493       +2     
  Lines       40555    40714     +159     
==========================================
+ Hits        23955    24070     +115     
- Misses      16600    16644      +44     

Impacted Files	Coverage Δ
dart/common/CAllocator.hpp	100.00% <ø> (ø)
dart/common/FreeListAllocator.cpp	74.57% <0.00%> (-5.43%)	⬇️
dart/common/FreeListAllocator.hpp	0.00% <ø> (ø)
dart/common/MemoryAllocator.hpp	100.00% <ø> (ø)
dart/common/PoolAllocator.hpp	0.00% <0.00%> (ø)
dart/common/CAllocator.cpp	71.92% <75.00%> (+0.81%)	⬆️
dart/common/PoolAllocator.cpp	75.00% <75.00%> (ø)
dart/common/detail/MemoryAllocator-impl.hpp	100.00% <0.00%> (ø)
dart/dynamics/EulerJoint.cpp	73.09% <0.00%> (+2.92%)	⬆️